The Applicant has developed the Netpage system, which is discussed below and discussed in detail in the cross-referenced documents identified herein. As the invention is particularly well suited to this system, it will be described in a Netpage context. However, it will be appreciated that hand-held optical sensing devices have broad ranging applications in many different fields and the invention is not limited to its use within the Netpage system.
The Netpage system involves the interaction between a user and a computer network (or stand alone computer) via a pen and paper based interface. The ‘pen’ is an electronic stylus with a marking or non-marking nib and an optical sensor for reading a pattern of coded data on the paper (or other surface).
One of the primary features of the Netpage pen is its ability to ‘click’ on interactive elements on a Netpage in the same way a mouse can click on screen-based interactive elements (e.g. hyperlinks and so on). However, with a Netpage pen, the user simply puts the nib on the interactive element in order to click on it. The optical sensor identifies the element via its unique page and location ID while a force sensor registers a ‘pen down’ condition when the nib is pressed against the page. Registering ‘pen down’ and ‘pen up’ is also fundamental to capturing the user's handwriting on Netpage input fields. Non-binary force signals are also captured for reproducing hand-drawn strokes with varying force-related width and opacity. Force variation can also be used as one of the parameters examined during signature verification.
The high tolerances and functionality required in force-sensing and image-sensing pens needs to be reconciled with the need for a pen, which is robust and easy for users to handle and transport.
Electronic image-sensing pens manufactured under license from Anoto, Inc. (see U.S. Pat. No. 7,832,361) typically use a force sensitive resistor for measuring nib force. However, force sensitive resistors have relatively long return-to-zero response times and are unsuitable for detecting end-strokes with a high degree of accuracy.